1. Field of the Invention
The present invention relates to electrical cables, and more particularly, to electrical cables having one or more inner conductors which are housed in an outer sheath.
Electrical cables are used to interconnect various electrical devices and terminals which are physically distant from each other. The cable carries electrical signals over one or more wires or conductors running the length of the cable, each of which is covered with a layer of insulating material. A male or female type connector is usually attached to each end of the cable. Each connector has a plug body to which the conductors of the cable are electrically connected. The plug body mates to a terminal or "jack" of the device being connected. The connector also usually has an outer cylindrical shell which protects the interconnection of the cable conductors to the plug body.
One type of cable, often referred to as an "audio cable", is extensively used to connect amplifiers to remote speakers and microphones as well as electrical musical instruments, such as electric guitars. Other uses of electrical cables include interconnecting video tape recorders to television receivers.
In order to prevent outside radio frequency (rf) noise from interfering with the signal transmitted over the cable, many cables have coaxial conductors which form an inner coaxial cable These coaxial cables have an inner strand of conductive wires surrounded by an insulating layer and then an outer layer of conductive wires. These outer wires are typically braided together to form a shield around the inner wires to reduce the interference to the inner wire signals caused by spurious rf noise
2. Description of the Prior Art
To protect the inner conductors, the electrical cable usually has a tough plastic or rubber sheath surrounding the conductors over the length of the cable. This outer sheath has typically been extruded directly onto the insulation covering the inner conductors, such that the conductors are tightly held within the sheath. However, even with this outer protective sheath, the inner conductors of the cable are often broken as a result of the stretching and bending normally encountered in normal use of the cable. This is particularly true for cables in which the conductors are made of strands or braids of fine copper wires as in many coaxial cables.
Since silver has a lower resistivity than copper, it would be desirable to plate the copper wires of a coaxial cable with silver in order to minimize the cable's electrical resistance and maximize the rejection rf of noise. However, because silver is relatively expensive, it is often not practical to use silver plated conductors where it is likely that the cable will not last.
Another problem experienced with coaxial cables is the tendency of the cable to "microphone" when bent. If the coaxial cable is sharply bent, the spacing between the inner strands and the outer shield can be significantly affected, thereby changing the capacitance of the coaxial cable. This can disrupt the signal transmission properties of the cable, which can be a siqnificant problem when transmitting audio signals over the cable.
In addition, many cables have a clamp at each end to clamp the end of the cable connector plug body. This clamp often cuts or wears through the outer sheath exposing the inner insulation and conductors, and causing the conductors to break.